As expressive as they are, things like overtone, supercollider, ChucK, pd, etc. always feel like a big teetering stack of dependencies that I don't really understand. So I eternally find myself trying to make a nice minimal simple synth I can drive from a MIDI keyboard.
To run:
export GOPATH=~/go # or something similar, wherever you want it
go get github.com/gordonklaus/portaudio
go get github.com/rakyll/portmidi
go run main.go
Sounds like: https://soundcloud.com/jcreed/himenepit https://soundcloud.com/jcreed/tell-me-some-time